There was Karl Marx…There was Friedrich Engels…And there was Mary Burns…Mary Burns? You don't see her portrait being paraded around Cuba or revered on stamps and coins. But when it comes to Salford's heritage she's the number one woman…And she was proper working class…

Yet no-one's ever heard of Mary Burns. And no-one can ever see her. She's a total mystery. There's no record of her birth, nor any surviving photos, and those who are into this stuff have spent years trying to find out more about her. Without a great deal of success.

What we do know is that she copped off with Fred Engels, lived with him for around twenty years, and without Mary Burns no-one would have found out about The Condition of the Working Class 1844 because she took him round and showed him the worst districts of Salford and Manchester for his research.

They say that if you can't change your doorstep you can't change the world. Basically, Mary showed Engels her doorstep and inspired him to change the world.

The only biographical reference to her was in two book about Engels, one by Max Beer in 1935 who wrote that Engels "lived in free union with an Irish girl of the people, Mary Burns, who had worked in his father's factory" and one by Edmund Wilson in 1941 who wrote that Engels "was having a love affair with an Irish girl named Mary Burns who worked in the factory of Ermen and Engels and had been promoted to run a new machine called a `self actor'. She seems to have been a woman of some independence of character as she is said to have refused his offer to relieve her of the necessity of working.

"She had, however, allowed him to set up her and her sister in a little house in the suburb of Salford where the coal barges and chimneys of Manchester gave way to the woods and fields...Mary Burns was a fierce Irish patriot and she fed Engels' revolutionary enthusiasm at the same time that she served him as a guide to the infernal abysses of the city."

Wilson gives no proof for all this, and Roy Whitfield in his book Friedrich Engels in Manchester, written in 1988, argued that Mary was actually from the Deansgate area on the Manchester side of the border with Salford, but accepted that his work was well researched speculation. Whitfield did, however, prove where she was born from the 1861 Census return when she gave her age as 38 and her birthplace as Manchester. Given that no-one knows where she actually lived, if Mary had pulled Fred while working in his Weaste factory, she was most likely to have lived in Salford.

The only direct reference to Mary Burns that survives is a letter from Marx to Engels on learning of her death saying she was "very good natured" and "witty", and a letter from Marx's daughter, Eleanor, saying that she was "very pretty, witty and an altogether charming girl…but in later years drank to excess." Sounds like she was, indeed, from Salford.

Mary Burns died on January 7 1863. No-one has ever found her grave. After Mary died, Fred lived with her sister, Lizzie, and married her on her deathbed.